Currently available hydraulic vehicle shock absorbers are most typically of the telescopic type in the form of a single piston and cylinder arrangement used in combination with a coil spring over the shock absorber. A piston rod is connected to the piston within the cylinder with its free end protruding from the cylinder for attachment to the body of the vehicle. The cylinder is attached to the vehicle wheel suspension. Extension or compression of the shock absorber, caused when the wheel suspension passes over a rough surface to elastically deform the coil spring, is damped by resistance to movement of the piston within the oil filled cylinder. The damping resistance to movement of the piston is provided by any of various forms of valve mechanism on the piston which restrict flow of the oil from one side of the piston to the other inside the cylinder.
The damping characteristics of the shock absorber can be adjusted to some degree through adjustment of the piston valve mechanism. Gas shock absorbers are also available which have the same basic structure outlined above, but are further provided with a gas chamber toward the end of the cylinder distal from the piston rod and separated from the oil filled chamber by an axially displaceable dividing piston. The gas pressure in the gas chamber can be adjusted to effect the dampening characteristics of the shock absorber.
These forms of currently available shock absorber suffer from various setbacks including limitations in adjustability to provide precise damping over specific ranges of wheel suspension movement amplitude and duration/frequency. The quality of ride provided by such shock absorbers is also typically compromised against vehicle handling performance.